Contractor forgot vapor barrier 2

[jimtheengineer10]

I received an email from a client saying the contractor forgot to put the vapor barrier under the concrete slab in their crawl space. They wanted to know if they should seal the concrete floor with something. Any thoughts on this?

 

[BUGGAR]

I do not necessarily disagree with this article. I will, however, put it to the test in any way I can. That is my responsibility as an Engineer.

 

[darthsoilsguy2]

on a side topic here.... everybody out there sells "services" or sells "product". i usually put more grains of salt on advice from people selling product. i can't think of any professor, instructor, and/or member of any committee like ACI/ASTM/etc... who doesn't do work for the private industry.... except people who are phasing themselves into retirement.

 

[thaidavid40]

If you absolutely gotta' have a vapor barrier, you could try injecting a bentonite slurry under the slab. Be careful not to overdo this, and accidentally jack the slab up so it cracks.
Dave

Thaidavid

 

[XR250]

what about coating the slab with a densifier?

 

[theonlynamenottaken]

Interesting digression in this thread in attacking Lstiburek for being both an expert and a consultant... Whether or not you accept his wisdom there is no question that Lstiburek is THE building science expert in conventionally built building envelopes.

If you are going to vent a crawlspace and let in moist air the vapor barrier should go on the bottom face of the floor framing envelope so all the condensation will form on top of your mudslab instead of the floor framing. If you don't want any condensation on your mudslab you should have insulated under that slab, though rigid board insulation on top of that slab may work for that?? As far as vapor barriers atop slab-on-grade:

Recent eng-tips thread on coating the top surface of S-O-G

See these links for good discussions on general crawlspace approaches, and on condensation in vented crawlspaces. Be warned -- after reading these you'll probably want to steer clear of crawlspaces altogether in the future!

New Light in Crawlspaces

Vented vs Unvented Crawlspaces

 

[Rabbit12]

I can't believe we still have people that don't believe what Lstiburek says in his article. He's right. There is an awful lot of research out there that supports his position.

 

[OldBldgGuy]

Lstiburek's style may not suit everyone, I find it wearing some times, but I had copies of papers published by him on building envelope issues back in the '80s and they have done a world of service to me and my clients since then. I'm in a very different climate than your crawlspace so I can't comment on it, but I'll tell you to believe Dr. Joe on envelope issues.

 

[BUGGAR]

O.K. I believe.

 

[Archie264]

Hey, I’m with you and I should have been clearer about that. I actually turned off the first lecture of his that I saw because I incorrectly thought he was selling LEED services with an attitude. Somehow I gave him a second chance and found that I did like green eggs with ham. I should have remembered that his style can be off-putting at first, though I’ve grown to enjoy it.

 

[jimtheengineer10]

I was told this was a crawl space but when I stopped by to take a look I found out it is a full basement. Does this change anyone's mind about things?

Are there any remedies other than tearing the slab out and redoing it?

 

[XR250]

what about coating the slab with a densifier? (repeated from before)